In cases where high supply voltage transients or spikes exist (such as automotive load-dump faults that be as larger as 40V), clamping voltages are sometimes forced to be above this level to avoid unintentional turn-on during such spikes. Referring to FIG. 1 of the drawings, the reference numeral 100 generally designates a conventional integrated circuit (IC) used in such an application. IC 100 generally includes a pin or terminal 108 that is generally coupled to an inductor L (such as a motor winding). For IC 100, when an actuation signal is provided through buffer 102 and resistor R1 to the control electrode or gate of transistor Q1 (which is generally an NMOS transistor), a circuit is completed between the voltage supply VCC and ground, energizing the inductor L. When transistor Q1 is deactuated, energy remains stored in inductor L, so as the magnetic field collapses, a fly-back current is generated in IC 100, which can damage transistor Q1.
To protect transistor Q1, a clamp is provided. The clamp generally comprises resistor R2 and diode stacks 104 and 106. The fly-back current traverses resistor R2 and the reversed biased zener diodes of stack 106, which reduces the voltage level of the fly-back current. This reduced voltage level of the fly-back current is further reduced by the forward bias diodes of stack 104, so that transistor Q1 can be actuated to discharge the energy stored in the inductor L. Once discharged, transistor Q1 is safely deactuated.
While this configuration does aptly discharge the inductor L, it does have limitations. Namely, for high reliability applications, such as automotive application, transistor Q1 must be very large (for example, 489,000 μm2). These very large transistor dimensions have become a severe limiting factor in the design of more compact high reliability ICs.
Some examples of conventional circuits are: A. Danchiv, “Protection functions in integrated low side switches,” Int. Semiconductor Conf. CAS, vol. 2, pp. 513-516, September 2007; W. Horn, and P. Singerl, “Thermally optimized demagnetization of inductive loads,” Proc. Euro. Solid-State Circuits, pp. 243-246, September 2004; M. Han, “A new soft self-clamping scheme for improving the self-clamped inductive switching (SCIS) capability of automotive ignition IGBT,” Int. Symp. Power Semiconductor Devices and ICs, pp. 145-148, May 2007; C. Ionascu, “Design aspects for gate driver of power switch,” Int. Semiconductor Conf. CAS, vol. 2, pp. 505-508, September 2007; M. Wendt, L. Thoma, B. Wicht, and D. Schmitt-Landsiedel, “A configurable high-side/low-side driver with fast and equalized switching delay,” IEEE J. Solid-State Circuits, vol. 43, no. 7, pp. 1617-1625, July 2008; W. C. Dunn, “Driving and protection of high side NMOS power switches,” IEEE Trans. Industry Applications, vol. 28, no. 1, pp. 26-30, January 1992; R. Gariboldi and F. Pulvirenti, “A 70 m intelligent high side switch with full diagnostics,” IEEE J. Solid-State Circuits, vol. 31, no. 7, pp. 915-923, July 1996; R. W. Adams, J. H. Carpenter, and T. Tanaka, “Low-side power output drive stage design and development concern,” Proc. IEEE Bipolar/BiCMOS Circuits and Technology Meeting, pp. 74-81, 2000; J. Wouters, J. Sevenhans, S. Hoogenbemt, T. Fernandez, J. Biggs, C. Das, and S. Dupont, “A novel active feedback flyback with only 100 mV inductive overshoot for a standard low-voltage CMOS inductive load driver, in a single-chip controller for 73 relays in a POTS/ADSL splitter application,” IEEE J. Solid-State Circuits, Vol. 40, No. 7, pp 1541-1549, July 2005; U.S. Pat. Nos. 4,695,770; 5,001,373; 5,723,916; 5,764,088; 5,812,006; 5,920,224; 6,078,204; 6,091,274; 6,580,321; 6,617,906.